Successfully delivering intensive yet safe gait therapy to individuals with significant walking deficits presents the greatest challenges to even the most skilled therapists. In the acute stages of many neurological injuries such as stroke, spinal cord injury, or traumatic brain injury, individuals often exhibit highly unstable walking patterns and poor endurance, making it difficult to safely practice gait for both the patient and therapist. Because of this, there has been a big push in rehabilitation centers to move over-ground gait training to the treadmill where body-weight support systems can help minimize falls while at the same time raising the intensity of the training. Numerous studies have investigated the effectiveness of body-weight supported treadmill training and have found that this mode of gait training promotes gains in walking ability similar to or greater than conventional gait training. Unfortunately there is a gap in technologies on the market for transitioning subjects from training on a treadmill to safe, weight-supported over-ground gait training. Practicing walking over-ground is critical, as our recent studies have demonstrated key differences between walking on a treadmill and walking over-ground. Additionally, treadmill walking does not allow individuals to practice Activities of Daily Living (ADLs), such as sit-to-stand, stairs, uneven terrain, or getting up off the floor. Since a primary goal of all individuals with walking impairments is to walk in their homes and in the community, it is imperative that therapeutic interventions involve ADL-based over-ground gait training. Since the summer of 2005, we have been developing an over-ground body-weight support gait training system called ZeroG, which provides individuals with gait impairments dynamic unloading of a percentage of their body-weight as they practice walking over-ground as well as balance and postural activities. The system, which rides along an overhead rail, provides both static and dynamic unloading, and has an active trolley such that the system automatically follows the subject as they walk. Here, a small motor drives the system so that it stays directly above the subject as they walk over-ground, or can be positioned in front of or behind the subject to resist or facilitate motion. With ZeroG, individuals with the most significant gait impairments can safely practice walking, balance and postural tasks early after their injuries. During our Phase I SBIR, we enhanced the trolley tracking capabilities of ZeroG by reconfiguring the system with a larger motor, developed and tested a more accurate and robust tracking algorithm, and conducted tests with the new system verifying our desired performance criteria were all met. The new system allows subjects to walk at faster speeds, and the additional force capabilities help to control the forward momentum of the subject during falls and for stabilization when lifting the subject from their wheelchair or off the floor. In addition, the improved performance of the system will now allow us to develop more advanced training activities that simulate ADLs, which may lead to enhanced therapeutic benefits. The goals of this Phase II SBIR are to extend the capabilities of ZeroG in terms of both performance as well as usability. Specifically, we will develop advanced ADL-based training modes such as sit-to-stand, sit-to-stand- to-step, stand-to-sit and an adaptive controller that automatically regulates body-weight support based on the subject's walking performance. We will also develop a wireless interface for ZeroG, allowing therapists to control all aspects of the system without having to be in front of the user-interface. Finally, we will develop training modules that detail various training activities therapists can practice with their patients, ranging from easy activities (e.g. sitting balance, trunk control) to high-level activities (e.g. balance platforms, side-to-side cross-over walking, etc). Adding advanced training activities to ZeroG will allow individuals with lower limb impairments the ability to safely practice over-ground gait, as well as postural and dynamic balance tasks, making it one of the most versatile gait training systems in the world. Additionally, adding a wireless interface as well as detailed training modules will ensure that therapists fully utilize the capabilities of the system. We believe that individuals who train with ZeroG will experience enhanced gains in over-ground walking ability and balance control when compared to existing conventional rehabilitation strategies as ZeroG will allow therapists to train patients through a broad spectrum of activities early after neurological injuries in a safe, controlled manner. ZeroG can be used in the functional rehabilitation of various disabling conditions, including stroke and spinal cord injury to amputations and with elderly individuals at risk for falls or following orthopedic injuries. In addition to clinical benefits, a body-weight support system of this nature can also be used to foster new research studies that focus on gait impairments and balance issues.